Light source

Light source device which can be used as a replacement light source for an ArI excimer laser. The light emitted from a Nd:YAG laser light source (L1) is incident on a nonlinear optical crystal (C1) and produces a second harmonic which is transmitted to a titanium-sapphire laser light source (L2). The light emitted by the titanium-sapphire laser light source (L2) is incident on nonlinear optical crystals (C2, C3) by which coherent light (W2) as the third harmonic is obtained. Light with a summed frequency of 193 nm is obtained by the means for producing a summed frequency (C4). Furthermore, by vector-phase matching the decrease of the conversion efficiency due to heat-induced phase-mismatch can be reduced. In addition, instead of the Nd:YAG laser light source a laser light source such as Nd:YLF, Nd:YVO4 or the like and instead of the titanium-sapphire laser light source (L2) a photoparametric oscillator can be used.